1. Field of the Invention
The invention in general relates to hydraulic fluid supplies, and more particularly to an arrangement used in the underwater environment at shallow to moderate depths and wherein a pump supplies hydraulic fluid to a load.
2. Description of Related Art
Various underwater vehicles have hydraulically activated mechanisms which require the supply of a hydraulic fluid. The hydraulic fluid is supplied by a motor driven pump which has a supply line and a return line wherein the return line pressure is controlled by the ambient sea pressure and the supply pressure is a fixed differential pressure above the return pressure.
The pump may be carried on the outside of the vehicle or in a free flooded compartment within the vehicle and in order to reduce pump noise radiation to the surrounding water medium, and to protect the pump body and shaft seal from seeing an excessive differential pressure, a double enclosure acoustic isolation arrangement is provided.
In such arrangement, the pump/motor unit is placed within a first pressure vessel filled with hydraulic fluid at the return line pressure and this pressure vessel in turn is enclosed within a second and larger pressure vessel filled with a gas at a nominal pressure of one atmosphere.
Although radiated pump noise is significantly reduced, the arrangement is bulky, heavy and difficult to make and assemble.
An improved system for reducing radiated pump noise is described and claimed in co-pending application Ser. No. 232907 filed Apr. 25, 1994, and assigned to the same assignee as the present invention. In that improvement, the dual pressure vessel arrangement is replaced by a single pressure vessel, the interior of which is maintained at a predetermined pressure by means of a gas supply and pressure regulator. The pressure within the return line, as well as operation of the regulator, is controlled by a reservoir having a piston and rod arrangement acted upon by the ambient water pressure.
Such arrangement is capable of deep diving operations such as 20,000 feet. The present invention eliminates the gas pressurization arrangement and is ideally suited for operation at shallower depths utilizing the same pump characteristics for the deeper diving system.